Representation of Women Among Grand Rounds Speakers at an Academic Health System Early in the COVID-19 Pandemic

Introduction An invitation to speak at grand rounds (GR) is considered an honor and an activity important for academic promotion. The aim of this study was to determine the representation of women among invited speakers at departmental GR and assess the impact of the COVID-19 pandemic on it. Methods We conducted a retrospective descriptive study on gender differences in all GR speakers between January 2019 and June 2021 at an academic health system in Western Massachusetts. We calculated the overall percentage of women presenters and compared it with the percentage of women faculty at our institution and nationally. To evaluate the impact of COVID-19 on this association, we calculated the absolute percentage difference between women and men speakers using the date of March 13, 2020, as the cut-off and conducted a sensitivity analysis using June 15, 2020, as the cut-off. Results During the study period, 46% (276/607) of GR speakers at our institution were women. This percentage reflected the percentage of the women faculty overall at our institution and was similar to women's representation among faculty nationally. Departments with high percentages of women faculty (Obstetrics and Gynecology, 76%; Pediatrics, 65%) had high percentages of women GR speakers (Obstetrics and Gynecology, 70%; Pediatrics, 51%; Psychiatry, 62%). COVID-19 did not appear to significantly influence gender representation among speakers. Conclusion At our institution, less than half of the GR speakers were women. However, this percentage appears to reflect the overall percentage of women faculty. Potential barriers and opportunities resulting from the COVID-19 pandemic did not appear to impact this finding.

Mass isotopomer study of anaplerosis from propionate in the perfused rat heart

Anaplerosis from propionate was investigated in rat hearts perfused with 0-2mM [(13)C(3)]propionate and physiological concentrations of glucose, lactate, and pyruvate. The data show that when the concentration of [(13)C(3)]propionate was raised from 0 to 2mM, total anaplerosis increased from 5% to 16% of the turnover of citric acid cycle intermediates. Then, [(13)C(3)]propionate abolished anaplerosis from endogenous substrates, glucose, lactate, and pyruvate. Also, while the contents of propionyl-CoA and methylmalonyl-CoA increased with [(13)C(3)]propionate concentration, the content of succinyl-CoA decreased, presumably via activation of succinyl-CoA hydrolysis by a decrease in free CoA. Under our conditions, [(13)C(3)]propionate was a purely anaplerotic substrate since there was no labeling of mitochondrial acetyl-CoA, reflected by the labeling of the acetyl moiety of citrate.

Competition between acetate and oleate for the formation of malonyl-CoA and mitochondrial acetyl-CoA in the perfused rat heart

We previously showed that, in the perfused rat heart, the capacity of n-fatty acids to generate mitochondrial acetyl-CoA decreases as their chain length increases. In the present study, we investigated whether the oxidation of a long-chain fatty acid, oleate, is inhibited by short-chain fatty acids, acetate or propionate (which do and do not generate mitochondrial acetyl-CoA, respectively). We perfused rat hearts with buffer containing 4 mM glucose, 0.2 mM pyruvate, 1 mM lactate, and various concentrations of either (i) [U-(13)C]acetate, (ii) [U-(13)C]acetate plus [1-(13)C]oleate, or (iii) unlabeled propionate plus [1-(13)C]oleate. Using mass isotopomer analysis, we determined the contributions of the labeled substrates to the acetyl moiety of citrate (a probe of mitochondrial acetyl-CoA) and to malonyl-CoA. We found that acetate, even at low concentration, markedly inhibits the oxidation of [1-(13)C]oleate in the heart, without change in malonyl-CoA concentration. We also found that propionate, at a concentration higher than 1 mM, decreases (i) the contribution of [1-(13)C]oleate to mitochondrial acetyl-CoA and (ii) malonyl-CoA concentration. The inhibition by acetate or propionate of acetyl-CoA production from oleate probably results from a competition for mitochondrial CoA between the CoA-utilizing enzymes.

Parenteral and enteral metabolism of anaplerotic triheptanoin in normal rats

A new chronic treatment for inherited disorders of long-chain fatty acid oxidation involves administering up to one-third of dietary calories as triheptanoin, a medium-odd-chain triglyceride (Roe CR, Sweetman L, Roe DS, David F, and Brunengraber H. J Clin Invest 110: 259-269, 2002). Heptanoate and C(5)-ketone bodies derived from its partial oxidation in liver are precursors of anaplerotic propionyl-CoA in peripheral tissues. It was hypothesized that increasing anaplerosis in peripheral tissues would boost energy production. In the present study, we tested the potential of a triheptanoin emulsion as an intravenous nutrient. Normal rats were infused with triheptanoin intravenously or intraduodenally at up to 40% of caloric requirement. The blood concentration ratio (heptanoate/C(5)-ketone bodies) was high with intravenous and low with intraduodenal triheptanoin infusion. During intravenous infusion of triheptanoin, lipolysis was stimulated but appeared compensated by fatty acid reesterification. During intraduodenal infusion of triheptanoin, lipolysis was not stimulated. Our data support the hypothesis that intravenous triheptanoin could be used to treat decompensated patients with long-chain fatty acid oxidation disorders.

Peroxisomal and mitochondrial oxidation of fatty acids in the heart, assessed from the 13C labeling of malonyl-CoA and the acetyl moiety of citrate

We previously showed that a fraction of the acetyls used to synthesize malonyl-CoA in rat heart derives from partial peroxisomal oxidation of very long and long-chain fatty acids. The 13C labeling ratio (malonyl-CoA)/(acetyl moiety of citrate) was >1.0 with 13C-fatty acids, which yields [13C]acetyl-CoA in both mitochondria and peroxisomes and < 1.0 with substrates, which yields [13C]acetyl-CoA only in mitochondria. In this study, we tested the influence of 13C-fatty acid concentration and chain length on the labeling of acetyl-CoA formed in mitochondria and/or peroxisomes. Hearts were perfused with increasing concentrations of labeled docosanoate, oleate, octanoate, hexanoate, butyrate, acetate, or dodecanedioate. In contrast to the liver, peroxisomal oxidation of 1-13C-fatty acids in heart does not form [1-13C]acetate. With [1-13C]docosanoate and [1,12-13C2]dodecanedioate, malonyl-CoA enrichment plateaued at 11 and 9%, respectively, with no detectable labeling of the acetyl moiety of citrate. Thus, in the intact rat heart, docosanoate and dodecanedioate appear to be oxidized only in peroxisomes. With [1-13C]oleate or [1-13C]octanoate, the labeling ratio >1 indicates the partial peroxisomal oxidation of oleate and octanoate. In contrast, with [3-13C]octanoate, [1-13C]hexanoate, [1-13C]butyrate, or [1,2-13C2]acetate, the labeling ratio was <0.7 at all concentrations. Therefore, in rat heart, (i) n-fatty acids shorter than 8 carbons do not undergo peroxisomal oxidation, (ii) octanoate undergoes only one cycle of peroxisomal beta-oxidation, (iii) there is no detectable transfer to the mitochondria of acetyl-CoA from the cytosol or the peroxisomes, and (iv) the capacity of C2-C18 fatty acids to generate mitochondrial acetyl-CoA decreases with chain length.

Regulation of malonyl-CoA concentration and turnover in the normal heart

The goal of this study was to test the relationship between malonyl-CoA concentration and its turnover measured in isolated rat hearts perfused with NaH(13)CO(3). This turnover is a direct measurement of the flux of acetyl-CoA carboxylation in the intact heart. It also reflects the rate of malonyl-CoA decarboxylation, i.e. the only known fate of malonyl-CoA in the heart. Conditions were selected to result in stable malonyl-CoA concentrations ranging from 1.5 to 5 nmol.g wet weight-(1). The malonyl-CoA concentration was directly correlated with the turnover of malonyl-CoA, ranging from 0.7 to 4.2 nmol.min(-) (1).g wet weight(-1) (slope = 0.98, r(2) = 0.94). The V(max) activities of acetyl-CoA carboxylase and of malonyl-CoA decarboxylase exceeded the rate of malonyl-CoA turnover by 2 orders of magnitude and did not correlate with either concentration or turnover of malonyl-CoA. However, conditions of perfusion that increased acetyl-CoA supply resulted in higher turnover and concentration, demonstrating that malonyl-CoA turnover is regulated by the supply of acetyl-CoA. The only condition where the activity of malonyl-CoA decarboxylase regulated malonyl-CoA kinetics was when the enzyme was pharmacologically inhibited, resulting in increased malonyl-CoA concentration and decreased turnover. Our data show that, in the absence of enzyme inhibitors, the rate of acetyl-CoA carboxylation is the main determinant of the malonyl-CoA concentration in the heart.

Peroxisomal fatty acid oxidation is a substantial source of the acetyl moiety of malonyl-CoA in rat heart

Little is known about the sources of acetyl-CoA used for the synthesis of malonyl-CoA, a key regulator of mitochondrial fatty acid oxidation in the heart. In perfused rat hearts, we previously showed that malonyl-CoA is labeled from both carbohydrates and fatty acids. This study was aimed at assessing the mechanisms of incorporation of fatty acid carbons into malonyl-CoA. Rat hearts were perfused with glucose, lactate, pyruvate, and a fatty acid (palmitate, oleate or docosanoate). In each experiment, substrates were (13)C-labeled to yield singly or/and doubly labeled acetyl-CoA. The mass isotopomer distribution of malonyl-CoA was compared with that of the acetyl moiety of citrate, which reflects mitochondrial acetyl-CoA. In the presence of labeled glucose or lactate/pyruvate, the (13)C labeling of malonyl-CoA was up to 2-fold lower than that of mitochondrial acetyl-CoA. However, in the presence of a fatty acid labeled in its first acetyl moiety, the (13)C labeling of malonyl-CoA was up to 10-fold higher than that of mitochondrial acetyl-CoA. The labeling of malonyl-CoA and of the acetyl moiety of citrate is compatible with peroxisomal beta-oxidation forming C(12) and C(14) acyl-CoAs and contributing >50% of the fatty acid-derived acetyl groups that end up in malonyl-CoA. This fraction increases with the fatty acid chain length. By supplying acetyl-CoA for malonyl-CoA synthesis, peroxisomal beta-oxidation may participate in the control of mitochondrial fatty acid oxidation in the heart. In addition, this pathway may supply some acyl groups used in protein acylation, which is increasingly recognized as an important regulatory mechanism for many biochemical processes.